The objectives are to quantify and to examine the interactions of receptors on the human red cell membrane with antibodies, lectins and drugs. The methods used for quantitation and topography include radioiodinated and enzyme-labeled antibodies and measurements of hemagglutination in the AutoAnalyzer continuous flow system. Endocytosis induced by the action of drugs is used for studying the behavior of membrane surface receptors especially as influenced by changes in metabolic activity and disease affecting red cell morphology. Toluidine blue is used to measure changes in available red cell membrane surfaces. Changes occurring during storage in various preservative media are being investigated. The identification of blood group activity in solubilized red cell membrane components will be attempted. BIBLIOGRAPHIC REFERENCES: Lau, F.O., Lama, S.S., Greenwalt, T.J.: Erythrocyte membrane surface measurements using toluidine blue. Fed. Proc., 35:475, 1976 (abstract). Lau, F.O., Lama, S.S., Swierk, E. McF., Greenwalt, T.J.: Measurements of drug-induced endocytosis in human red blood cells. Clin. Research, 24:313A, 1976 (abstract).